Messy Christmas (2007) on Netflix

Jan and Sara have a patchwork family: Sara has been married three times before falling in love with Jan and she brought one child from every previous marriage into this family. Jan has only been married once before and he, too, brought a child into this family. Now, Sara invited all their ex-spouses along with their new partners and children to celebrate Christmas with them. While they are makes jibes at each other, Sara reveals that she is pregnant with Jan's child - except Jan has sterilized himself without telling Sara. Who is the father of his child? All of Sara's ex-husbands are immediately suspect and Jan is adamant about finding out.